Manufacture of perforated acoustic bodies



Jun 1964 o. w. AKERSON MANUFACTURE OF FERF'ORATED ACOUSTIC BODIES 2 Sheets-Sheet 1 Filed Oct. 6, 1958 In yen for Jazz/ad Wflkersoiz differ 71% June 16, 1964 n. w. AKERSON 3,137,364

MANUFACTURE OF PERFORATED ACOUSTIC BODIES Filed Oct. 6, 1958 2 Sheets-Sheet 2 E (DR|1 ED) IJJ 25.. Q Q 9 Q B(cAvlTlzEo) Ll-J o 20- u C(NoN-cAvlTlzeo) 15 Lu I I X 15 1e 17 18 19 A|R-DRY DENSITY (POUNDS PER CUBIC FooT) Eye United States Patent The present invention relates to acoustic material and in particular to the manufacture of acoustic bodies or panels, such as wallboard, tile and plank.

I-Ieretofore, porous panel-form bodies which have interior capacity to absorb sound have been drilled with holes to collect sound waves and transmit them to the interior of the body. The common practice is to drill round holes of such size that they are visible when present in ceiling tile, and the arrangement of the holes is such as to form an acceptable pattern.

Where visibility of such holes is undesired, as for example, when other decoration is present at the surface of the tile, a recent practice is to punch small holes with pins or needles, of such diameter that the holes are practically invisible at viewing distance, or otherwise if visible, constitute such a small portion of the containing area that other decoration at the surface subdues the visible effect of such small holes.

The present invention aims to improve the sound absorbing capacity of bodies such as ceiling tile in which such small holes are present in the surface for soundabsorption.

It is an object of the invention to provide at the interior of a porous sound-absorbing body a multiplicity of soundabsorbing cavities so located that each is in communication with the exterior by a channel of relatively smaller size, terminating in a small opening in the surface.

It is a particular object of the invention to provide a cavity wholly inward from both faces of an integral soundabsorbing panel.

It is also among the objects of the invention to provide various methods for producing such openings and cavities in sound-absorbing bodies of various materials.

It is a particular object of the invention to produce such openings in the interior of an integral felted fiber body containing vegetable fibers.

It is also a particular object of the invention to provide means for producing cavitized surface openings in vegetable fiber panels.

Various other and ancillary objects and advantages of the invention will appear from the following description and explanation of the invention as set forth in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary perspective view partly in crosssection showing a face with openings therein and illustrating two types of cavity formation which occur in a vegetable fiber panel.

FIG. 2 is a view similar to FIG. 1 showing the type of cavity formation in a mineral fiber tile.

FIG. 3 is a graph showing the variation in absorption by a series of products similar to FIG. 1, which vary in density.

FIG. 4 shows a modification of structure in which two cavities similar to that of FIG. 1 merge into a single cavity.

FIG. 5 shows the preferred punch for vegetable fiber board.

It is to be understood that the drawings are merely illustrative and are not intended to limit the invention.

In testing the sound-absorbing capacity of fiber board,

' such as used in acoustic tile, it was found that the members of a series of like tile with the same pattern of surface openings of the same size, varied greatly in their of the punch, the innermost one being the smaller.

3,137,364 Patented June 16, 1964 ICC sound absorbing capacity. It was determined that the character of the punch used to make the holes was a controlling factor.

Investigation of the variations of punch structure showed that some punches merely pushed the fibers aside forming a hole matching the punch in contour. Other punches formed a cavity within the board larger in size than the opening formed in the surface by the punch. Other punches delaminated the fiber body.

For example, withreference to a wood fiber insulation board of about 17 lb. per cu. ft. density, the following observations were made:

Blunt punches, that is, cylindrical rods with a flat circular end, tend to delaminate the structure by pushing an area of felted layers inwardly, which pushed area carries with it adjacent structure felted into it. With a diameter of 3 inch the effect was barely noticeable. At. /s inch diameter, delamination is easily observed. At inch diameter the punch completely destroyed the neighboring structure of the board.

Pointed punches having a long taper, with an included angle in the vicinity of 10 to 15 merely formed a hole in size corresponding to the shape of the punch. Pointed punches having an included angle of 45 delaminated the board like a fiat-end punch. Pointed punches having a short taper at an included angle in the vicinity of 30 formed within the board a cavity of larger size than the hole formed in the surface, the cavity being connected to the exterior by a short tubular channel in the surface layer. j t

It was discovered that when such a cavity-forming short-tapered punch was provided with a fiat end, by grinding off the point, preferably, but not necessarily, at right angles to the axis of the punch, a pear-shaped cavity is formed near but inwardly from the surface opening and the cavity is larger than when the punch is not flattened and is pointed. In some instances such punches also form two spaced pear-shaped cavities alined along the path The presently preferred punch for mechanical reasons as well as for the formation of cavities in a vegetable fiber board is a cylindrical one having a diameter of 5 inch, with a frusto-conical end with a small base having a diameter of 0.015 to 0.020 inch and a wall with an included cone angle of 30. It appears that the delaminating tendency above referred to enhances the cavitizing action of a pointed punch. The small flat area of the advancing punch is too small to destroy the board, but it has a rupturing action leading to a larger cavity being formed by the following tapered section. Circular punches are preferred so that the cavity formed is more or less symmetrically pear-shaped, and also for mechanical facility in providing a gang punch and stripper plate.

The action of cavitizing above described in part depends upon the tensile strength and toughness of individual vegetable fibers which are pulled out of their original felted positions in cavitizing, and compressed in the lower part of the cavity. Sometimes there is a densified body of fiber along the lower portion of a side wall, and sometimes it is in the bottom of the channel left by the punch. When the felted body is made entirely of mineral fibers such as rock wool, the action is diiferent. Mineral fibers are relatively brittle, and break, rather than yield to displacement by the punch.

, In cavitizing mineral tile a different form of punch is used. The shape of the cross-section is not important. It may be square, triangular, star-shaped or other irregular form. It may be used without taper and the end may be flat or notched or otherwise varied. A fiat end may be either at right angles to the axis or inclined relative to it, thus forming a sharp angular edge to advance into the enemas d) mineral felt. The advancing edges of the punch at the top layer of the tile cause breakage of fibers to form an entering tubular channel corresponding to the largest cross-section of the tapered portion of the punch. The broken fibers are pushed ahead of the advancing face, either directly or at an angle, and these aid the punch in breaking more fibers but at regions laterally of the path of the punch. Thus, a ragged cavity results of size relatively larger than the size of the punch and of the entering opening in the surface.

The cavities formed vary individually in size and shape, apparently as a result of variations locally in the board structure. Sometimes, the internal structure is such that a cavity does not form, but because such fiber boards are relatively homogeneous, the punching of a large number of holes in the same manner assures that substantially all of them have a cavity. The aim is to provide a multiplicity of cavities each connected to at least one of a multiplicity of surface openings. In general, the cavities correspond to the characteristics shown in FIG. 1 and FIG. 2.

FIG. 1 represents a fragmentary enlarged view of a vegetable fiber board cavitized as described. The body has felted wood fibers bonded by having hydrated the fibers before felting, pressing and drying to a density of about 17 lbs/cu. ft. Such boards are commonly coated for decoration with coating material which forms a coat substantially non-absorbentof sound, as indicated by the coat 11. The coated face is punched as described forming a multiplicity of openings, some being indicated at 12, and others at 13 and 14.

The opening 13 extends as a tubular channel 15 through the coating and through the adjacent layer of the fiber body. Then, the enlarged cavity 16 which is formed is generally pear-shaped tapering in the direction away from the surface to a tubular channel 17 at the bottom of the cavity substantially matching the punch size. The darkened area 18 represents one location at which a densified fiber mass is deposited. Thus, the cavity has a major portion of its wall area at least as porous as the body of the board with the sound-absorbing porosity of the Wall area in communication with the porosity of the body.

Some holes formed in the same manner as hole 13, and at the same time in the same board, show two cavities, as illustrated at the opening 14. The upper cavity 20 corresponds generally to cavity 16, but below it there is a tubular channel 21 generally matching the punch in size which channel 21 enlarges to a cavity 22, smaller than cavity 20 and likewise pear-shaped, which second cavity is extended by tubular channel 23 formed by the end of punch. The local variations in formation account for the different results.

In FIG. 2, the numeral 30 represents a tile in which all the fibers are mineral, such as glass fiber or rock wool, with a decorative coat 31. Merely for the purpose of illustration the surface openings are varied, being circular at 32 and 33, triangular at 34- and square at 35, made with fiat-end rods or punches as described. Opening 33 is one end of a tubular channel 37 with walls extending normal to the face of the tile, the cross-section of said channel matching the punch size through the coating and through the surface layer of'the body, and then within the body the channel enlarges at its other end into a ragged cavity 38 extending substantially entirely to its bottom 39.

When the body portion is made of mixed rock wool fibers and sulfite fibers, for example, in the proportion of 85 to 15 parts, respectively, the cavity formation responds very closely to that of FIG. 2, due to the predominance of the mineral fibers.

Although the cavitized holes are preferably formed in a gang in a suitable press, they may be formed individually and by hand. In so using a hand punch in a vegetable fiberboard, an experienced operator feels the formation of a cavity. At first there is a build-up of resistance to the pressing force, then the resistance weakens and the punch moves in. The release of resistance indicates the formation of a cavity. In the case of mineral fiber felts, there is no corresponding reaction.

The character of the cavity varies with the density of the board punched. A board of any given density when uncompressed may be compressed within limits and punched while so compressed. Thus, in using a gang punch with a stripper plate through which the punches extend, the character of the cavity may be varied by varying the degree of compression of the board while being punched. This may be accomplished by placing the stripper plate in contact with the face to be punched at varying pressures from zero to some higher pressure, before moving the punches into the board. Pressure of the stripper plate on the punched face is important to prevent lifting of the coating at the edge of a hole by the outwardly moving punch. Compression of a coated board before punching is frequently important to prevent breaking the coat at regions away from the entering punch, depending in part on the density of the board and in part on the character of the coat, for example, its brittleness.

The density of the board is involved in its sound-absorbency. Sound-absorbency is measured in several different ways of which one has been used for testing products of the present invention, namely the impedance tube test of American Society of Testing Materials, designation C 384-561 An area of a board is tested for sound in the following frequencies: 250, 500, 1000 and 2000 cycles per second, and the test values found for each of said frequencies are averaged as tube test coefficient, hereinafter referred to as TTC.

Wood fiber boards of various densities and of one-half inch thickness, all coated, were gang-punched and cavitized with -inch diameter punches with the 30 frustoconical end previously described in a random arrangement of 578 holes per sq. ft. FIG. 3 shows the TTC for the various densities. The significance of the results is. indicated by the fact that substantially the same values are secured by the same test, using boards of the same char acter drilled in a random manner with At-inch and 7 inch diameter drills totaling 319 holes per sq. ft. whereas for the non-cavitized punching, much less absorption occurs.

FIG. 3 is a plot of TTC on the Y axis against density of the board on the X axis, the density being for airdry wood fiber board in pounds per cu. ft. Graph A represents the TTC for boards with the conventional drilled holes, with a random and mixed pattern of two sizes of drills namely fit-inch and -inch diameter.

Graph B is a plot of TIC in similar boards cavitized with the preferred type of blunted tapered -inch diameter punch above described. It has nearly the same capacity for absorption as the drilled units, but has the advantage of practically invisible openings at viewing distances in a completed installation.

Graph C represents the TTC of similar units punched with non-cavitizing tapered punches of -inch diameter. The appearances of the units for graphs B and C are identical, and the value of the interior cavities is represented by the higher TTC values of graph B over graph C.

Two or more openings may be formed so that their companion cavities merge. FIG. 4 shows such a case in a wood fiber board 41 with coat-ing ill and two openings 42 and 43, with tubular channels 44 and 45 so closely positioned and cavitized that one cavity 46 is formed by merger of two, the cavity having two tubular channels 47 and 48 at its bottom matching the end of the punches When a mineral fiber board is to be cavitized to produce cavities larger than those described in FIG. 2, the body of the board may be made with a great number of shot such asthe globules formed with mineral fibers, which are larger in diameter than a rod-punch to form holes in the surface. By chance distribution, the rod punches may engage shot and push the same inwardly to form cavities. Such use of shot must be purposeful and is to plicity of cavities, each communicating by a tubular channel with at least one such opening, each cavity being of relatively larger size than the one or more channels communicating therewith, which enhance the sound-absorbing capacity because of the internal enlargement of the entering channel.

The form of the cavity may vary greatly, the important point being that it opens to the atmosphere through an opening which is smaller in cross-section than the cavity Within the body, the preferred form having a tubular channel providing an elongated bottle-neck opening, and

accordingly, they are herein designated as bottle-shaped.

The invention may be embodied in numerous ways without departing from the spirit and scope of the invention as expressed in the appended claims.

I claim:

1. An acoustical material comprising a rigid integral body portion having sound-absorbing porosity and having a soundq'eceiving face, a coat on said face which is substantially non-absorbent with respect to sound, said face having a multiplicity of sound-receiving openings, said openings being the outer ends of tubular channels in said body portion and through said coat, said channels having walls extending normal to said face in an appreciably thick layer of said body portion, said body portion inwardly of said layer having cavities wholly within said bod-y portion, said cavities being enlargements in the direction parallel to said face of the inner ends of said tubular chan nels, a substantial portion of the Wall area of each cavity being a porous sound-absorbing surface communicating with the porosity of said body portion.

2. An acoustical material according to claim 1 in which the body portion is a porous fiber felt.

3. An acoustical material according to claim 1 in which the body portion is a porous felt of vegetable fiber.

References Cited in the file of this patent UNITED STATES PATENTS 518,766 Plecker Apr. 24, 1894 891,516 Abery June 23, 1908 1,682,986 Rymarczick Sept. 4, 1928 2,045,099 Pond June 23, 1936 2,412,713 Burt Dec. 17, 1946 2,459,121 Willey et a1 Jan. 11, 1949 2,562,711 Gessler et al July 31, 1951 2,615,525 Berner Oct. 28, 1952 2,657,759 Creamer Nov. 3, 1953 2,667,925 Dalphone Feb. 2, 1954 2,668,123 Copeland Feb. 2, 1954 2,684,093 Enzmann et a1 July 20, 1954 2,968,327 Mariner Jan. 17, 1961 3,013,626 Brown et a1 Dec. 19, 1961 3,017,947 Eckert Jan. 23, 1962 FOREIGN PATENTS 642,722 Great Britain Sept. 13, 1950 

1. AN ACOUSTICAL MATERIAL COMPRISING A RIGID INTEGRAL BODY PORTION HAVING SOUND-ABSORBING POROSITY AND HAVING A SOUND-RECEIVING FACE, A COAT ON SAID FACE WHICH IS SUBSTANTIALLY NON-ABSORBENT WITH RESPECT TO SOUND, SAID FACE HAVING A MULTIPLICITY OF SOUND-RECEIVING OPENINGS, SAID OPENINGS BEING THE OUTER ENDS OF TUBULAR CHANNELS IN SAID BODY PORTION AND THROUGH SAID COAT, SAID CHANNELS HAVING WALLS EXTENDING NORMAL TO SAID FACE IN AN APPRECIABLY THICK LAYER OF SAID BODY PORTION, SAID BODY PORTION INWARD LY OF SAID LAYER HAVING CAVITIES WHOLLY WITHIN SAID BODY PORTIONS, SAIDCAVITIES BEING ENLARGEMENTS IN THE DIRECTION PARALLEL TO SAID FACE OF THE INNER ENDS OF SAID TUBULAR CHANNELS, A SUBSTANTIAL PORTION OF THE WALL AREA OF EACH CAVITY BEING POROUS SOUND-ABSORBING SURFACE COMMUNICATING WITH THE POROSITY OF SAID BODY PORTION. 